Hi, my son was also not crawling at that time, at 6 months he also did not really want to roll over or spend any time on his front. We got prescribed to see a physiotherapist to check nothing was wrong and to give us some tips.
she checked him for any damage to his back or hips and it was all ok thankfully. Then she showed us some moves to do with him that were not as severe as just putting him on his front as he would always cry.
the best exercise was to use a firm cushion or mat (they had one from ikea that was folded so it turned into a step about 15cm high) and put the baby there so that the arms and chest were on the top and legs on the floor, like they were crawling up the step. Putting some toys up there really helped him.
Also holding him so he has to do some work with his core muscles, or leaning him on his side against your leg was good. Thinking about it, you can even do the first exercise with your legs as the step too.
after a couple of months of doing this he suddenly started crawling, it was amazing how quickly he did it! So that was at about 10 months in the end.
the physiotherapist said it is better that a child starts crawling before walking because they develop a better coordination where they use both sides of their body. He started walking at about 15 months and is very active and coordinated now at 2 years!
i wish you the best, let me know if you want any more details about the exercises.😊